1. Field of the Invention
The present invention relates to an image inspection system for effecting a quality control process on color display units including color television sets, color cathode-ray tubes, display monitor units, projection-type display units, etc.
2. Description of the Prior Art
For the quality control of color display units, it is necessary to inspect displayed images on those color display units for geometric raster distortions, color purity, convergence, focus, etc. on the display screens of the color display units. One conventional image inspection apparatus for inspecting such displayed images uses a video camera to image an arbitrary test chart displayed on a display screen to be inspected and processes an image signal generated by the video camera to inspect the display screen.
In the conventional image inspection apparatus, inspected (measured) results are displayed as shown in FIG. 1 of the accompanying drawings. As shown in FIG. 1, an area A surrounded by a peripheral outer frame and a peripheral inner frame is displayed on the inspected display screen, and contains dots "a" representative of measured results of outermost measurement spots. Nine reference circles B1.about.B9 are displayed in a central area on the display screen which is surrounded by the area A, and contain respective dots b1.about.b9 representative of measured results of measurement spots in the central area.
If the dots "a" are linearly displayed centrally in the area A, then it can be determined that the peripheral area of the screen is of good quality. If the dots b1.about.b9 are displayed at the respective centers of the reference circles B1.about.B9, then it can be determined that the central area of the screen is of good quality.
When human vision is relied upon to determine whether the dots "a" are linearly displayed centrally in the area A and also whether the dots b1.about.b9 are displayed at the respective centers of the reference circles B1.about.B9, decisions may suffer individual differences introduced by the operators. Stated otherwise, the array of dots "a", for example, is relatively unclear to the human eye for making a decision as to whether it is straight or not.
If the dots "a" are displaced out of the area A or the dots b1.about.b9 are displayed out of the respective reference circles B1.about.B9, then the display screen is judged as being defective. In a quality control process associated with a manufacturing process, it is general practice to establish two decision standards, i.e., adjustment standards and inspection standards, which are different from each other and used to make respective quality decisions. It is tedious and time-consuming and tends to be misleading the operator to display both the area A and the reference circles B1.about.B9 simultaneously for each of the adjustment standards and the inspection standards.
For establishing the decision standards, the dots "a", "b" are marked with measurement numbers, and reference values are entered at those numbered dots "a", "b" on a standard setting table as shown in FIG. 2 of the accompanying drawings. However, the process of entering the standard data is not easy to carry out because the reference values have to be entered while paying attention to the positions and numbers of the dots.
If the number of measurement spots is increased in an attempt to improve the quality control, then it will become difficult to decide how those measurement spots are associated with the numbers of the dots and it will need more manual work to enter reference values at the dots. Furthermore, the increased number of measurement spots is apt to make the displayed dots more unclear to the human eye. If an increased number of reference circles are displayed, they will look too crowded in the limited space on the display screen and be susceptible to observational errors.
It has also been proposed to display measured results as graphic patterns which have modeled an enlarged image of measurement spots, meter-like graphic patterns, or web-shaped graphic patterns. However, any of these proposed graphic patterns have failed to clearly display the measured results and to allow the operator to make decisions with ease.